More

Seismic Safety Concerns Found At Calero Reservoir

SAN JOSE (KCBS) – New restrictions are being imposed on Santa Clara County’s Calero Reservoir because of seismic safety concerns.

Water levels are being lowered 20 feet from the crust because of new data, which shows gravel and sand from the underlying creek bed could make the dam vulnerable during a major quake.

KCBS’ Mike Colgan Reports:

Frank Maitski, who oversees dam safety for the Santa Clara Valley Water District, told board members that it’s not just the magnitude of an earthquake that is concerning, but the duration as well.

“In terms of Loma Prieta in ’89, it was fairly far away from this particular dam,” Maitski said. “It was only 15 seconds and earthquakes could go a lot longer than that. I believe the 1906 earthquake was well over a minute. It’s really the duration, not just at the peak. How long that shaking is occurring really affects the stability of the structure.”

Maitski said the primary concern for Calero Dam is the Shannon Fault, which could generate a 6.7 magnitude event about a mile from the dam.

A similar problem was discovered at the Anderson Dam in Santa Clara County in October.